Plaster Testing:

     Ingredients

     Test batches

Applying Plaster:

    Techniques

    Case Study

As I was just getting familiar with earthen plasters, I wanted to create a simple demo wall using the three best recipes from my test batches.  The exact recipes that I used are particular to my ingredients, but I will offer my recipes if you would like a better feel for the ratios.

Step 1: Ingredients -paper pulp, horse manure, cow manure, sand, and clay

First, I gathered my ingredients, which were already prepared for mixing, and set to work measuring out the right proportions of sand and clay onto a tarp.  After mixing the sand and clay until it was consistent, I added the right portions of fiber (cow, horse or paper pulp), and continued to mix.

 

Step 11: Mixing- sand & clay first, then add the fiber

Mixing the ingredients together on the ground by dancing on them is the easiest and most fun technique.  By rolling the tarp over and making a plaster "burrito", you can gather the materials and mix them further. 

 

Step 111: Prepare to Apply- wet the surface and add bonding layer if necessary.

In order to make my plaster stick to this brick wall, I had to add a bonding layer.  I wanted to try the plaster on both chicken wire and burlap sack, so I bolted both to the wall using a drill and masonry fixtures.  I also used nuts as spacers to allow a little room between the wire and the wall. 

 

Step 1V: Apply the Plaster- by hand and smooth with a trowel

After mixing up my three best recipes, I applied them by hand to the wall.  I found that the wire worked much better, because the sack was wav--no matter how much I bolted it down-- and the plaster would just flake off of it.  It was very difficult to work on this surface as opposed to a cob or straw bale base.  I also was not working on a very good foundation.  I laid down a layer of coarse sand underneath my plasters, but I still had to make the bottom most plaster very thick in order to work my way up the wall.  For this reason, the final product was not exactly uniform, but slanted.

The final product can be seen at Humboldt State University's Campus Center for Appropriate Technology.

references & special thanks:

Lonny Grafman, personal communication; Glenn Howe, personal communication; Jeff Adams, personal communication

The Last Straw http://www.thelaststraw.org/bonus-articles/earthplaster.html

Earthen Clay Plasters and Aliz http://www.nmclay.com/Customer_service/Earthenplaster.htm